A 13-year-old boy was killed by a roadside bomb as he walked to school in the southern city of Basra, one of 20 victims of violence that continued to rattle Iraq Sunday while political leaders remained deadlocked over a new government.

The explosion occurred at 7:30 a.m. as children were arriving for class in the center of Basra, about 340 miles southeast of Baghdad, police Capt. Mushtaq Kadim said. The school week begins Sunday and runs through Thursday in Iraq, where Friday is the day of prayer for Muslims.

The attack was part of a startling increase in violence recently against Iraqi citizens. In the capital Sunday, a bomb also exploded in front of a house in the central neighborhood of Karradah, killing a woman and wounding two of her sisters and a man next door, police said.

Police discovered nine bodies, handcuffed and bullet-riddled, dumped in south Baghdad's Dora neighborhood - victims of execution-style killings. And security guards for the Iraqi finance minister were attacked while driving in western Baghdad before they had picked up the minister. One guard was killed, while a bystander was wounded, police said.

A group of visiting U.S. politicians voiced alarm a day earlier about rising sectarian violence in Iraq and told Iraqi leaders they needed to urgently overcome their stalemate and form a national unity government.

It was the second high-level U.S. delegation in less than a week to deliver the same stark message to Iraqi politicians as the Bush administration steps up pressure to overcome the political impasse that threatens to scuttle hopes to start an American troop pullout this summer.

"We need very badly to form this unity government as soon as possible," Sen. John McCain, R-Ariz., said at a news conference Saturday after meeting with President Jalal Talabani and Prime Minister Ibrahim al-Jaafari. "We all know the polls show declining support among the American people."

U.S. Ambassador Zalmay Khalilzad, who has patiently shepherded negotiations to form a new government, already was looking beyond that task to the need to cap the sectarian, militia-inspired killing.

"More Iraqis are dying today from the militia violence than from the terrorists," Khalilzad told reporters during a visit to a sports complex refurbished with American aid. "This will be a challenge for the new government - what to do about the militias."

The country's leadership must "overcome the strife that threatens to rip apart Iraq," he said.

Nevertheless, a sixth session of multiparty meetings Saturday failed to overcome the logjam that has snarled formation of a government for more than three months.

Sen. Russell Feingold, of Wisconsin and the ranking Democrat in the U.S. delegation, joined McCain in pressing for the quick formation of a government but spoke bluntly of his concern that the continued presence of American forces was prolonging the conflict.

"It's the reality of a situation like this that when you have a large troop presence that it has the tendency to fuel the insurgency because they can make the incorrect and unfair claim that somehow the United States is here to occupy this country, which of course is not true," he said.

On Tuesday, a delegation led by Sen. John Warner, the Virginia Republican who is chairman of the Armed Services Committee, delivered the same tough message, saying the uneasiness back home could force U.S. lawmakers to press for a reduction in American troop strength if the government delay were prolonged - regardless of the consequences.

With November's midterm congressional elections drawing nearer and American voters increasingly disenchanted with the Iraq war, the two visits in quick succession by high-powered U.S. politicians signaled deep concern over potential fallout from a lack of progress in Iraq.

Talabani, a Kurd, has formed a coalition with Sunni and secular politicians against a second term for al-Jaafari, a move that only deepened the government stalemate more than three months after the Dec. 15 parliamentary elections.

The U.S. politicians met separately with each of the men, as well as the U.S. commander in Iraq, Gen. George Casey.

Seven people - most civilians killed in their homes by mortar fire - died Saturday and several others were wounded in a gunbattle between forces of the Shiite Mahdi Army militia and Sunni insurgents near Mahmoudiya, about 20 miles south of the capital.

At least 13 other people were killed in scattered violence Saturday and two more bodies were found dumped in the capital, shot in the head with their hands and feet bound.